Communications system

ABSTRACT

A communication system is disclosed comprising an X2 gateway, a number of base stations, and a mobile device. The base stations are able to establish X2 connections directly with each other or via the X2 gateway. Various procedures are disclosed to determine how X2 connections should be established based on compatibility of the respective base stations with the X2 gateway.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 14/893,173 filed on Nov. 23, 2015, U.S. Pat. No.10,004,103 issued on Jun. 19, 2018, which is a National Stage Entry ofInternational Application PCT/JP2014/063630, filed on May 16, 2014,which claims the benefit of priority from United kingdom PatentApplication 1309970.0 filed on Jun. 4, 2013, the disclosures of all ofwhich are incorporated in their entirety by reference herein.

TECHNICAL FILED

The present invention relates to a communications system and tocomponents thereof for providing communication services to mobile orfixed communication devices. The invention has particular, but notexclusive, relevance to the discovery of transport network layer (TNL)addresses used by base stations in Long Term Evolution (LTE) Advancedsystems as currently defined in associated 3rd Generation PartnershipProject (3GPP) standards documentation; and to the use of the TNLaddresses for setting up X2 interfaces between neighbouring basestations.

BACKGROUND ART

In a cellular communications network, user equipment (UE) (such asmobile telephones, mobile devices, mobile terminals, etc.) cancommunicate with other user equipment and/or remote servers via basestations. LTE systems include an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN) and an Evolved Packet Core (EPC) network (orsimply ‘core network’). The E-UTRAN includes a number of base stations(‘eNBs’) for providing both user-plane (e.g. Packet Data ConvergenceProtocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC)and PHYsical (PHY) layers) and control-plane (e.g. Radio ResourceControl (RRC)) protocol terminations towards the UE.

In order to provide seamless connectivity for the mobile devices, thebase stations are configured with a list of their neighbour basestations so that the mobile devices can be handed over to one of thecells operated by other base stations when necessary (e.g. due tomobility of the mobile devices and/or changes in signal conditionsand/or load balancing, etc). Therefore, each base station is required tostore information relating to its neighbours including, inter alia,identifiers of the cells operated by each (known) neighbour basestation, a unique identifier (e.g. eNB Id) associated with eachneighbour base station, and a respective transport network layer (TNL)address associated with each neighbour base station. The TNL addressfacilitates communication between base stations via a so-called X2interface, which is provided between each neighbour base station pair.The X2 interface uses the Stream Control Transmission Protocol (SCTP) totransmit data between the base stations.

Each base station can obtain the TNL address associated with anotherbase station by following a so-called TNL Address Discovery procedurespecified in section 22.3.6 of 3GPP TS 36.300 V11.5.0, the contents ofwhich are incorporated herein by reference. In summary, whenever aparticular base station discovers a ‘candidate’ neighbour base station,it can request the so-called Mobility Management Entity (MME) in thecore network to transfer configuration information between the two basestations via an S1 interface (which is provided between each basestation and the core network). This procedure needs to be followedwhenever there is a change in the configuration of one of the basestations and/or whenever a base station or a cell is added to (orremoved from) the network to prevent handover problems for the mobiledevices (e.g. incorrect selection of a handover target cell, which mightresult in loss of connection) in the vicinity of such cells. Sinceconventional (macro) base stations operate in an always-on mode andtheir configuration does not change often, this procedure does not causeunnecessary load on the core network elements and the S1 interfacebetween the eNB s and the MME.

The 3GPP standards body has adopted an official architecture and definedstandards for home base stations (‘HNB’). Where a home base station isoperating in accordance with the LTE standards, the home base station issometimes referred to as a HeNB. A similar architecture is also appliedin the WiMAX network. In this case, the home base station is commonlyreferred to as a femto cell. For simplicity, the present applicationwill use the term HeNB to refer to any such home base station and willuse the term eNB generically to refer to other base stations (such asthe base station for the macro cell in which a HeNB operates). The HeNBcan provide radio coverage (for example, 3G/4G/WiMAX) via one or morecells within a home, small and medium enterprise environment, and/or inpublic places (such as shopping malls and the like). The HeNB connectsto the core network via a suitable public network (for example via anADSL link to the Internet) or operator network and in the case of the3GPP standards, via a so called small cell gateway (e.g. including thefunctionality of a so called HeNB-GW) which typically aggregates trafficfrom several HeNBs.

SUMMARY OF INVENTION Technical Problem

Network operators are facing a number of challenges due to HeNBdeployment. For example, the HeNBs are typically under the operationalcontrol of a customer rather than the network operator. Unlike eNBs, thehome base stations may power on and off frequently (e.g. gracefully forenergy saving reasons and/or abruptly for any other reasons) causingfrequent configuration changes in the neighbouring (home) base stations(i.e. to add/remove the cell(s) operated by these home base stationsand/or to update the corresponding X2 connections). In a worst casescenario, after a power ON/Off cycle, the TNL Address of a HeNB maychange (because the address assignment might be the responsibility ofanother provider, e.g. an Internet service provider, ISP). Hence, e.g.in the morning/evening when it becomes active in a typical homeenvironment, every HeNB triggers a TNL Address Discovery process ondiscovering each of its neighbours, which are most likely the sameneighbours as before. Although each HeNB discovers a small number ofneighbours only, on a national level it can be in the order of millions,depending on the number of households operating their own HeNB.

Another challenge resulting from the high number of HeNBs is that eachbase station (i.e. eNB/HeNB) needs to maintain a large number of X2connections (i.e. one with each of its neighbour eNBs/HeNBs). In orderto reduce the number of X2 connections to be maintained in an eNB, aso-called X2-Gateway (X2-GW) entity (which may form part of or may beseparate from the small cell gateway) can be provided between the eNBsand a predetermined group of HeNBs. In particular, the X2-GW makes itpossible for an eNB to establish a single X2 connection with the X2-GWfor each of a plurality of HeNBs that are also connected to that X2-GW.

To support the use of such an X2-GW, a modified TNL address discoveryprocedure has been proposed that is based on the TNL discovery proceduredescribed above (referred to hereafter as the “legacy TNL addressdiscovery procedure”). In the modified TNL address discovery procedure,the HeNB returns the TNL address of the X2-GW instead of its own TNLaddress. However, the inventors have identified a number of problemswith the current proposals:

-   -   1) Whenever an eNB discovers an HeNB, if the HeNB returns the        TNL address of the X2-GW to the eNB and the eNB does not support        X2-GW operability, then the process will fail as the eNB is not        able to establish a connection via the X2-GW.    -   2) Whenever an HeNB discovers an eNB and the eNB does not        support X2-GW operability, if the HeNB tries to establish a        connection to the eNB via the X2-GW, then the process will fail.    -   3) Whenever a source HeNB discovers a target HeNB, if the source        HeNB tries to establish the X2 connection via the X2-GW and the        target HeNB does not support the X2-GW, then the process will        fail.

Solution of Problem

The inventors have made a number of improvements that try to alleviateone or more of these problems.

According to one aspect, the present invention provides a source basestation for use in a communication system having a plurality of otherbase stations, the source base station comprising: a neighbour discoverymodule for discovering a neighbouring target base station; and a networkaddress discovery module for sending, towards the target base station, aconfiguration request message for requesting network address informationrelating to the target base station; wherein the network addressdiscovery module is arranged to include information in saidconfiguration request message indicating whether or not the source basestation supports use of an X2 gateway device through which an X2connection can be established between the source base station and thetarget base station.

The network address discovery module may be arranged to receive aconfiguration response message sent from the target base station, whichconfiguration response message includes network address informationrelating to the target base station and information indicating whetheror not the target base station supports use of an X2 gateway devicethrough which the X2 connection can be established between the sourcebase station and the target base station. In this case, theconfiguration response message sent by the target base station mayinclude a network address of an X2 gateway device supported by thetarget base station. A network connection module may also be providedthat establishes a network communication link with the X2 gateway devicesupported by the target base station using the network address includedin the configuration response message. In one embodiment, the sourcebase station registers with the X2 gateway device supported by thetarget base station using the network address included in theconfiguration response message. In an alternative embodiment, theconfiguration response message sent by the target base station includesa network address of the target base station.

The source base station may include, in said configuration requestmessage, a network address for an X2 gateway device with which thesource base station has a network communication link.

The source base station may further comprise an X2 setup module arrangedto send the target base station an X2 setup request message via said X2gateway device over the established network communication link. The X2setup module may include the network address of the target base stationin the X2 setup request message so that the X2 gateway device canestablish a network connection with the target base station. The X2setup request message may also include an identifier that identifies thetarget base station to which the X2 gateway device should send the X2setup request message. Preferably each subsequent X2AP message includesan identifier that identifies the source base station.

In one embodiment, the X2 setup module receives, from the X2 gatewaydevice, an X2 setup response message sent by the target base station, tocomplete the establishment of an X2 connection between the source basestation and the target base station through the X2 gateway device.

The network address information relating to the target base stationincluded in the configuration response message depends upon whether ornot both the source base station and the target base station support theuse of an X2 gateway device through which the X2 connection between thesource base station and the target base station can be established.

The source base station is arranged to determine whether or not toinclude an identifier for the target base station in subsequent X2communication messages transmitted over the X2 connection establishedbetween the source base station and the target base station dependingupon information included in or absent from the configuration responsemessage.

For example, the source base station may be arranged to include anidentifier for the target base station in subsequent X2 communicationmessages transmitted over the X2 connection established between thesource base station and the target base station if information includedin the configuration response message indicates that the target basestation supports use of the X2 gateway device; and is arranged not toinclude the identifier for the target base station in subsequent X2communication messages transmitted over the X2 connection establishedbetween the source base station and the target base station if theconfiguration response message does not include information indicatingthat the target base station supports the use of the X2 gateway device.

The source base station may also be arranged to include an identifierfor the source base station in subsequent X2 communication messagestransmitted over the X2 connection if it determines to include anidentifier for the target base station.

The identifier for the target base station may comprise a radio networklayer address or ID.

The invention also provides a target base station for use in acommunication system having a plurality of other base stations, thetarget base station comprising: a communications control module arrangedto receive a configuration request message sent by a source base stationand arranged to send, towards the source base station, a configurationresponse message having address information relating to the target basestation; wherein the communications control module is arranged toinclude information in said configuration response message indicatingwhether or not the target base station supports use of an X2 gatewaydevice through which an X2 connection can be established between thesource base station and the target base station.

The configuration response message may include a network address of anX2 gateway device supported by the target base station. Alternatively,the configuration response message may include a network address of thetarget base station.

The configuration request message may include a network address for anX2 gateway device with which the source base station has a networkcommunication link and the target base station may register with the X2gateway device using the address included within the configurationrequest message.

Typically, the target base station will include an X2 setup modulearranged to receive, via said X2 gateway device, an X2 setup requestmessage from the source base station. In this case, the X2 setup modulemay send, via the X2 gateway device, an X2 setup response message to thesource base station, to complete the establishment of an X2 connectionbetween the source base station and the target base station through theX2 gateway device.

The X2 setup module may include an identifier of the source base stationin the X2 setup response message so that the X2 gateway device can sendthe X2 setup response message to the source base station. Typically, theX2 setup response message includes an identifier that identifies thetarget base station.

In one embodiment, the network address information relating to thetarget base station included in the configuration response messagedepends upon whether or not both the source base station and the targetbase station support the use of an X2 gateway device through which theX2 connection between the source base station and the target basestation can be established. The target base station may determinewhether or not to include an identifier for the source base station insubsequent X2 communication messages transmitted over the X2 connectionestablished between the source base station and the target base stationdepending upon information included in or absent from the configurationrequest message. For example, the target base station may include anidentifier for the source base station in subsequent X2 communicationmessages transmitted over the X2 connection established between thesource base station and the target base station if the informationincluded in the configuration request message indicates that the sourcebase station supports use of the X2 gateway device; and does not toinclude the identifier for the source base station in subsequent X2communication messages transmitted over the X2 connection establishedbetween the source base station and the target base station if theconfiguration request message does not include information indicatingthat the target base station supports the use of the X2 gateway device.The target base station may also be arranged to include an identifierfor the target base station in subsequent X2 communication messagestransmitted over the X2 connection if it determines to include anidentifier for the source base station. The identifier for the sourcebase station may be a radio network layer address or ID.

According to another aspect, the present invention provides a sourcebase station for use in a communication system having a plurality ofother base stations, the source base station comprising: a neighbourdiscovery module for discovering a neighbouring target base station; andan X2 setup module arranged to send, without performing a networkaddress discovery procedure for the target base station, an X2 setuprequest to an X2 gateway device associated with the source base station;wherein the X2 setup request is arranged to include an identifier forthe target base station for use by the X2 gateway device to determine ifthe target base station supports X2 connection setup through the X2gateway device.

In the event that an X2 setup failure message is received from the X2gateway device indicating that the target base station does not supportuse of the X2 gateway device, the source base station may be arranged totrigger a network address discovery procedure to determine a networkaddress for the target base station in order to establish a direct X2connection with the target base station.

According to another aspect, the present invention provides an X2gateway device for use in a communication system having a plurality ofbase stations, the X2 gateway device comprising: a base stationregistration module for registering one or more base stations with theX2 gateway device; a memory having base station data for registered basestations, the base station data including network address data andidentifier data for each registered base station; and an X2 setup modulefor receiving an X2 setup request message from a source base stationthat is registered with the X2 gateway device, the X2 setup requestmessage including an identifier for a target base station; wherein theX2 setup module is arranged to use the identifier for the target basestation in the received X2 setup request message to determine if thebase station data in said memory includes a network address for thetarget base station.

If the X2 setup module determines that the base station data in saidmemory does not include a network address for the target base station,the X2 setup module may send the source base station an X2 setup failuremessage with a cause of failure indicating that the target base stationdoes not support X2 connection through the X2 gateway device.

If the X2 setup module determines that the base station data in saidmemory does include a network address for the target base station, theX2 setup module may send the X2 setup message from the source basestation to the target base station using the network address containedin said base station data.

According to another aspect, the present invention provides a sourcebase station for use in a communication system having a plurality ofother base stations, the source base station comprising: a neighbourdiscovery module arranged to discover a neighbouring target basestation; and an X2 setup module arranged: i) to send an X2 neighbournotify message to an X2 gateway device associated with the source basestation, the X2 neighbour notify message including an identifier for thetarget base station for use by the X2 gateway device to determine if thetarget base station supports X2 connection setup through the X2 gatewaydevice; and ii) to receive a notification from the X2 gateway deviceindicating whether or not the target base supports X2 connection throughthe X2 gateway device.

The X2 setup module may be arranged to send, in the event that thenotification received from the X2 gateway device indicates that thetarget base station supports X2 connection through the X2 gatewaydevice, an X2 setup request message to the X2 gateway device, the X2setup request message including an identifier for the target basestation. In the event that the notification received from the X2 gatewaydevice indicates that the target base station does not support use ofthe X2 gateway device, the source base station may trigger a networkaddress discovery procedure to determine a network address for thetarget base station in order to establish a direct X2 connection withthe target base station.

According to another aspect, the present invention provides an X2gateway device for use in a communication system having a plurality ofbase stations, the X2 gateway device comprising: a base stationregistration module for registering one or more base stations with theX2 gateway device; a memory having base station data for registered basestations, the base station data including network address data andidentifier data for each registered base station; and an X2 setup modulearranged: i) to receive an X2 neighbour notify message from a sourcebase station, the X2 neighbour notify message including an identifierfor a target base station; ii) to use the identifier for the target basestation in the received X2 neighbour notify message to determine if thebase station data in said memory includes a network address for thetarget base station; and iii) to send the source base station anotification indicating whether or not the target base supports X2connection through the X2 gateway device depending on whether or not thebase station data in said memory includes a network address for thetarget base station.

The X2 setup module may be further arranged: iv) to receive an X2 setuprequest message from the source base station, the X2 setup requestmessage including an identifier for a target base station; v) toretrieve a network address for the target base station from said basestation data; and vi) to send the X2 setup request to the target basestation using the retrieved network address for the target base station.If the X2 setup module determines that the base station data in saidmemory does not include a network address for the target base station,the X2 setup module may send the source base station a notificationindicating that the target base station does not support X2 connectionthrough the X2 gateway device.

According to another aspect, the present invention provides a sourcebase station for use in a communication system having a plurality ofother base stations, the source base station comprising: means fordiscovering a neighbouring target base station; and means for sending,towards the target base station, a configuration request message forrequesting network address information relating to the target basestation; wherein the means for sending is arranged to includeinformation in said configuration request message indicating whether ornot the source base station supports use of an X2 gateway device throughwhich an X2 connection can be established between the source basestation and the target base station.

According to another aspect, the present invention provides a targetbase station for use in a communication system having a plurality ofother base stations, the target base station comprising: means forreceiving a configuration request message sent by a source base stationand for sending, towards the source base station, a configurationresponse message having address information relating to the target basestation; wherein the target base station is arranged to includeinformation in said configuration response message indicating whether ornot the target base station supports use of an X2 gateway device throughwhich an X2 connection can be established between the source basestation and the target base station.

According to another aspect, the present invention provides a sourcebase station for use in a communication system having a plurality ofother base stations, the source base station comprising: means fordiscovering a neighbouring target base station; and means for sending,without performing a network address discovery procedure for the targetbase station, an X2 setup request to an X2 gateway device associatedwith the source base station; wherein the X2 setup request is arrangedto include an identifier for the target base station for use by the X2gateway device to determine if the target base station supports X2connection setup through the X2 gateway device.

According to another aspect, the present invention provides an X2gateway device for use in a communication system having a plurality ofbase stations, the X2 gateway device comprising: means for registeringone or more base stations with the X2 gateway device; a memory havingbase station data for registered base stations, the base station dataincluding network address data and identifier data for each registeredbase station; and means for receiving an X2 setup request message from asource base station that is registered with the X2 gateway device, theX2 setup request message including an identifier for a target basestation; and

means for using the identifier for the target base station in thereceived X2 setup request message to determine if the base station datain said memory includes a network address for the target base station.

According to another aspect, the present invention provides a sourcebase station for use in a communication system having a plurality ofother base stations, the source base station comprising: means fordiscovering a neighbouring target base station; and means for sending anX2 neighbour notify message to an X2 gateway device associated with thesource base station, the X2 neighbour notify message including anidentifier for the target base station for use by the X2 gateway deviceto determine if the target base station supports X2 connection setupthrough the X2 gateway device; and means for receiving a notificationfrom the X2 gateway device indicating whether or not the target basesupports X2 connection through the X2 gateway device.

According to another aspect, the present invention provides an X2gateway device for use in a communication system having a plurality ofbase stations, the X2 gateway device comprising: means for registeringone or more base stations with the X2 gateway device; a memory havingbase station data for registered base stations, the base station dataincluding network address data and identifier data for each registeredbase station; and means for receiving an X2 neighbour notify messagefrom a source base station, the X2 neighbour notify message including anidentifier for a target base station; means for using the identifier forthe target base station in the received X2 neighbour notify message todetermine if the base station data in said memory includes a networkaddress for the target base station; and means for sending the sourcebase station a notification indicating whether or not the target basesupports X2 connection through the X2 gateway device depending onwhether or not the base station data in said memory includes a networkaddress for the target base station.

According to another aspect, the present invention provides a methodperformed by a source base station of a communication system having aplurality of other base stations, the method comprising: discovering aneighbouring target base station; sending, towards the target basestation, a configuration request message for requesting network addressinformation relating to the target base station; and includinginformation in said configuration request message indicating whether ornot the source base station supports use of an X2 gateway device throughwhich an X2 connection can be established between the source basestation and the target base station.

According to another aspect, the present invention provides a methodperformed by a target base station of a communication system having aplurality of other base stations, the method comprising: receiving aconfiguration request message sent by a source base station; sending,towards the source base station, a configuration response message havingaddress information relating to the target base station; and includinginformation in said configuration response message indicating whether ornot the target base station supports use of an X2 gateway device throughwhich an X2 connection can be established between the source basestation and the target base station.

According to another aspect, the present invention provides a methodperformed by a source base station of a communication system having aplurality of other base stations, the method comprising: discovering aneighbouring target base station; sending, without performing a networkaddress discovery procedure for the target base station, an X2 setuprequest to an X2 gateway device associated with the source base station;and including in the X2 setup request, an identifier for the target basestation for use by the X2 gateway device to determine if the target basestation supports X2 connection setup through the X2 gateway device.

According to another aspect, the present invention provides a methodperformed by an X2 gateway device of a communication system having aplurality of base stations, the method comprising: registering one ormore base stations with the X2 gateway device; storing base station datafor registered base stations, the base station data including networkaddress data and identifier data for each registered base station; andreceiving an X2 setup request message from a source base station that isregistered with the X2 gateway device, the X2 setup request messageincluding an identifier for a target base station; and using theidentifier for the target base station in the received X2 setup requestmessage to determine if the base station data in said memory includes anetwork address for the target base station.

According to another aspect, the present invention provides a methodperformed by a source base station of a communication system having aplurality of other base stations, the method comprising: discovering aneighbouring target base station; and sending an X2 neighbour notifymessage to an X2 gateway device associated with the source base station,the X2 neighbour notify message including an identifier for the targetbase station for use by the X2 gateway device to determine if the targetbase station supports X2 connection setup through the X2 gateway device;and receiving a notification from the X2 gateway device indicatingwhether or not the target base supports X2 connection through the X2gateway device.

According to another aspect, the present invention provides a methodperformed by an X2 gateway device of a communication system having aplurality of base stations, the method comprising: registering one ormore base stations with the X2 gateway device; storing base station datafor registered base stations, the base station data including networkaddress data and identifier data for each registered base station;receiving an X2 neighbour notify message from a source base station, theX2 neighbour notify message including an identifier for a target basestation; using the identifier for the target base station in thereceived X2 neighbour notify message to determine if the stored basestation data includes a network address for the target base station; andsending the source base station a notification indicating whether or notthe target base station supports X2 connection through the X2 gatewaydevice depending on whether or not the stored base station data includesa network address for the target base station.

Aspects of the invention extend to computer program products such ascomputer readable storage media having instructions stored thereon whichare operable to program a programmable processor to carry out a methodas described in the aspects and possibilities set out above or recitedin the claims and/or to program a suitably adapted computer to providethe apparatus recited in any of the claims.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings in which:

FIG. 1 schematically illustrates a mobile telecommunication system of atype to which the invention is applicable;

FIG. 2 is a block diagram illustrating the main components of a basestation forming part of the system shown in FIG. 1;

FIG. 3 is a block diagram illustrating the main components of a homebase station forming part of the system shown in FIG. 1;

FIG. 4 is a block diagram illustrating the main components of a gatewayforming part of the system shown in FIG. 1;

FIG. 5 is an exemplary timing diagram illustrating a method performed bycomponents of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention;

FIG. 6 is an exemplary timing diagram illustrating a method performed bycomponents of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention;

FIG. 7 is an exemplary timing diagram illustrating a method performed bycomponents of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention;

FIG. 8 is an exemplary timing diagram illustrating a method performed bycomponents of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention;

FIG. 9 is an exemplary timing diagram illustrating a method performed bycomponents of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention;

FIG. 10 is an exemplary timing diagram illustrating a method performedby components of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention;

FIG. 11 is an exemplary timing diagram illustrating a method performedby components of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention;

FIG. 12 is an exemplary timing diagram illustrating a method performedby components of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention; and

FIG. 13 is an exemplary timing diagram illustrating a method performedby components of the mobile telecommunication system of FIG. 1 whilstcarrying out an embodiment of the invention.

DESCRIPTION OF EMBODIMENTS Overview

FIG. 1 schematically illustrates a mobile (cellular) telecommunicationsystem 1 including a mobile telephone 3 (or other compatible userequipment) served via a macro cell of one of the macro base stations 5-1or 5-2 (eNB) and/or home cells of a plurality of home base stations 7-1,7-2 or 7-3 (HeNBs). The telecommunication system 1 also comprises a corenetwork 9.

Each macro base station 5 and each home base station 7 is connected tothe core network 9 via an S1 interface. The core network 9 comprises,amongst other things, a mobility management entity (MME) 11. The basestations 5 and 7 are also connected to each other via a so-called X2interface, which is usually provided directly between each pair of(home) base stations. However, in this embodiment, an X2 gateway (X2-GW)13 entity is provided via which X2 connections can be made forcompatible macro base stations 5-1 and home base stations 7-1 and 7-2.The X2-GW 13 is also connected to the core network 9, e.g. via aninterface towards the MME 11. Legacy base stations (such as macro basestation 5-2 or home base station 7-3) cannot connect via the X2-GW 13,so their X2 connections are made directly with the corresponding otherbase station 5 or 7. This is illustrated in FIG. 1, for example, by thedirect X2 connection between HeNB 7-2 and HeNB 7-3.

As will be understood by those skilled in the art, each eNB 5/HeNB 7operates one or more cells in which communications can be made betweenthe eNB 5/HeNB 7 and the mobile telephone 3. A user of the mobiletelephone 3 can communicate with other users and/or remote servers viathe eNB 5/HeNB 7 and the core network 9. As those skilled in the artwill appreciate, whilst one mobile telephone 3, two macro base stations5-1 and 5-2, and three home base stations 7-1, 7-2, and 7-3 are shown inFIG. 1 for illustration purposes, the system, when implemented, willtypically include other mobile telephones and base stations.

Base Station

FIG. 2 is a block diagram illustrating the main components of one of themacro base stations (eNB) 5 shown in FIG. 1. As shown, the eNB 5includes transceiver circuitry 51 which is operable to transmit signalsto, and to receive signals from, the mobile telephone 3 via one or moreantennae 53 and which is operable to transmit signals to and to receivesignals from another base station 5, the HeNB 7, the X2-GW 13, and theMME 11 via a network interface 55. The operation of the transceivercircuitry 51 is controlled by a controller 57 in accordance withsoftware stored in memory 59. The software includes, among other things,an operating system 61, a communications control module 63, a neighbourdiscovery module 65, a TNL address discovery module 67, a networkconnection module 69 and an X2 setup module 70.

The communications control module 63 is operable to handle (e.g.generate, send and receive) control signals for controlling theconnections between the base station 5 and other entities, such as themobile telephone 3, other base stations, the mobility management entity11, and/or the X2-GW 13.

The neighbour discovery module 65 is operable to scan the base station's5 neighbourhood (without transmitting any data) in order to discoverneighbours in its vicinity. The neighbour discovery module 65 may alsobe operable to discover neighbours through other means, e.g. using itsAutomatic Neighbour Relation (ANR) functionality and/or a NetworkMonitor Mode (NMM) module.

The TNL address discovery module 67 is arranged to use a TNL addressdiscovery procedure to determine the TNL address of a new neighbouridentified by the neighbour discovery module 65.

The network connection module 69 is arranged to establish networkconnections (such as SCTP connections) with the discovered neighbour orX2-GW 13 (depending on the capabilities of each base station 5).

The X2 setup module 70 is arranged to establish an X2 connection withthe discovered neighbour either directly or via the X2-GW 13 (dependingon the capabilities of each base station 5).

Home Base Station

FIG. 3 is a block diagram illustrating the main components of one of thehome base stations (HeNB) 7 shown in FIG. 1. As shown, the HeNB 7includes transceiver circuitry 71 which is operable to transmit signalsto, and to receive signals from, the mobile telephone 3 via one or moreantennae 73 and which is operable to transmit signals to and to receivesignals from the eNB 5, another HeNB 7, the X2-GW 13, and the MME 11 viaa network interface 75. The operation of the transceiver circuitry 71 iscontrolled by a controller 77 in accordance with software stored inmemory 79. The software includes, among other things, an operatingsystem 81, a communications control module 83, a neighbour discoverymodule 85, a TNL address discovery module 87, a network connectionmodule 89 and an X2 setup module 90.

The communications control module 83 is operable to handle (e.g.generate, send and receive) control signals for controlling theconnections between the home base station 7 and other entities, such asthe mobile telephone 3, other base stations, the mobility managemententity 11, and/or the X2 gateway 13.

The neighbour discovery module 85 is operable to scan the home basestation's 7 neighbourhood (without transmitting any data) in order todiscover neighbours in its vicinity. The neighbour discovery module 85may also be operable to discover neighbours through other means, e.g.using ANR and/or NMM.

The TNL address discovery module 87 is arranged to use a TNL addressdiscovery procedure to determine the TNL address of a new neighbouridentified by the neighbour discovery module 85.

The network connection module 89 is arranged to establish networkconnections (such as SCTP connections) with the discovered neighbour orX2-GW 13 (depending on the capabilities of each base station 5).

The X2 setup module 90 is arranged to establish an X2 connection withthe discovered neighbour either directly or via the X2-GW 13 (dependingon the capabilities of each base station 5).

X2 Gateway

FIG. 4 is a block diagram illustrating the main components of the X2-GW13 shown in FIG. 1. As shown, the X2-GW 13 includes a network interface131 which is operable to transmit signals to, and to receive signalsfrom, the eNBs 5 and the HeNBs 7. The operation of the network interface131 is controlled by a controller 137 in accordance with software storedin memory 139. The software includes, among other things, an operatingsystem 141, a communication control module 143, a base stationregistration module 145, a network connection module 147 and an X2 setupmodule 149. The memory also holds mapping data 151 that maintains datarelating to base stations that are registered with the X2-GW 13.

The communications control module 143 is operable to handle (e.g.generate, send and receive) control signals for controlling theconnections between the X2-GW 13 and the base stations.

The base station registration module 145 is operable to register basestations (including eNBs 5 and HeNBs 7) that are currently powered onand have an SCTP association with the X2-GW 13 and to maintain a mappingtable indicating correspondence between RNL identities and TNL addressesof each base station registered with the X2-GW. This mapping table isstored in the base station data 151.

The network connection module 147 is operable to establish networkconnections with other entities using, for example, the SCTP protocol.In particular, the network connection module 147 is operable to create anetwork connection (communication link) between the X2-GW 13 and a basestation.

The X2 setup module 149 is arranged to establish an X2 connection with abase station on behalf of a registered base station.

In the above description, the base station 5, the home base station 7,and the X2-GW 13 are described for ease of understanding as having anumber of discrete modules (such as the communications control modules,the X2 setup modules, and the network connection modules, etc.). Whilstthese modules may be provided in this way for certain applications, forexample where an existing system has been modified to implement theinvention, in other applications, for example in systems designed withthe inventive features in mind from the outset, these modules may bebuilt into the overall operating system or code and so these modules maynot be discernible as discrete entities. These modules may also beimplemented in software, hardware, firmware or a mix of these.

Operation

The operation of the communication system will now be explained for anumber of different operating scenarios, in which one base station (asource base station) identifies a new neighbour base station (targetbase station):

Scenario #1: source=eNB and target=HeNB

Scenario #2: source=HeNB and target=eNB

Scenario #3: source=HeNB and target=HeNB

If both the source base station and the target base station arecompatible to operate through the X2-GW 13, then the X2 connectionbetween them should be through the X2-GW 13; otherwise if either or bothof the source base station and the target base station are notcompatible with the X2-GW 13, then a direct X2 connection should beestablished between them.

A number of different solutions will now be described that consider theabove scenarios:

Solution 1: considers Scenario #1 and Scenario #2

Solution 2: considers Scenario #3 (and possibly Scenario #1 and Scenario#2)

Solution 3: considers Scenario #3 (and possibly Scenario #1 and Scenario#2)

Solution 4: considers Scenario #1 and Scenario #2

Solution 1

In this solution, X2-GW information is exchanged between the source basestation and the target base station and a new Information Element (IE)is added in the X2 setup request message to allow the X2-GW to establishthe X2 connection between the source and target base stations.

Solution 1 (Scenario #1)

FIG. 5 is a timing diagram illustrating the steps performed using thissolution for Scenario #1 where the source is eNB1 5-1 (which supportsuse of the X2-GW 13) and the target is HeNB2 7-2 (which also supportsuse of the X2-GW 13). As shown in FIG. 5, at step s501, eNB1 5-1discovers HeNB2 7-2. At step s503, the eNB1 5-1 initiates a TNL addressdiscovery procedure by sending, to the MME 11, an 51 eNB ConfigurationTransfer message that includes the Global HeNB identifier (HeNB-ID2) ofHeNB2 7-2 (as the intended recipient of the message) and its own globaleNB identifier (eNB-ID1) as the message sender. The ConfigurationTransfer message also includes the Tracking Area Indicator (TAI2) forHeNB2, the TAI for eNB1 (TAI1) and a new Information element (IE1) thatindicates that eNB1 5-1 supports use of the X2-GW 13. The new IE1 may bea single bit flag whose value indicates support or non-support for theX2-GW 13. At step s505, the MME 11 sends the Configuration Transfermessage to the HeNB2 7-2.

Due to the presence of the new IE1 in the received ConfigurationTransfer message, and as HeNB2 7-2 also supports the use of the X2-GW13, HeNB2 7-2 can determine whether or not the source base station (eNB15-1) also supports use of the X2-GW 13. In this example, the source(eNB1) does support use of the X2-GW 13, and therefore, in step s507,the target HeNB2 7-2 responds by sending a Configuration Transfermessage back to MME 11, identifying the TNL address (TNL-GW) of theX2-GW 13 instead of its own TNL address. The HeNB2 7-2 also includes anew IE that indicates that the target HeNB2 7-2 supports use of theX2-GW 13 (and therefore indicating that the returned TNL address is thatof the X2-GW 13 with which HeNB2 is registered). In step s509, the MME11 sends the returned Configuration Transfer message to eNB1. In steps511, eNB1 determines from the returned Configuration Transfer messagethat HeNB2 also supports use of the X2-GW 13 and so uses the TNL addressreceived in the Configuration transfer message to establish an SCTPconnection with the X2-GW 13. Subsequently, in step s513, eNB1 sends anX2 Setup Request message to the X2-GW 13 over the SCTP connection it hasjust established with the X2-GW 13. This X2 Setup Request messageincludes a new IE (IE3) that includes the RNL-ID of the target basestation (HeNB2). The X2 Setup Request message already includes theRNL-ID of the source base station (eNB1), so this is not required in thenew IE3. The X2-GW 13 uses the RNL-ID of the target base station (HeNB2)to retrieve (from its stored mapping table) the corresponding TNLaddress of HeNB2 and in step s515, the X2-GW 13 forwards the X2 SetupRequest message received from eNB1 to HeNB2 using the retrieved TNLaddress. The target base station (HeNB2) determines the identity of thesource base station from the RNL-ID of the source base station that isalready included in the X2 Setup Request message and in step s517returns an X2 Setup Response message back to the X2-GW 13. This X2 SetupResponse message also includes a new IE (IE4) identifying the RNL-ID ofthe intended recipient of the message (i.e. source eNB1) as well as itsown RNL-ID address. The X2-GW 13 uses the intended recipient's RNL-ID toretrieve the corresponding TNL address from its stored mapping table andthen forwards the X2 Setup Response message to base station eNB1 usingthe retrieved TNL address of eNB1 (which it does in step s519). Basestation eNB1 uses the RNL-ID of the sender to identify the base stationsending the X2 Setup Response message to complete the X2 Setup procedurebetween eNB1 and HeNB2. In all subsequent X2 AP messages sent betweeneNB1 and HeNB2, the sender includes (for example in new IE4 or new IE5)the RNL-ID of the intended recipient base station and its own RNL-ID,and the X2-GW uses the intended recipient's RNL-ID to retrieve thecorresponding TNL address from its mapping table so that it can routethe message to the correct base station over the correct SCTPconnection.

If, on the other hand, HeNB2 7-2 does not support use of the X2-GW 13(because for example, it is a legacy device), then the HeNB2 wouldsimply ignore the new IE in the received Configuration Transfer messageand it would respond by including its own TNL address in the returnedConfiguration Transfer message and there will be no new IE in thereturned message, thereby indicating to eNB1 that HeNB2 does not supportuse of the X2-GW 13. In this case, therefore, the eNB1 would establish adirect SCTP connection with HeNB2 and then a direct X2 connection withHeNB2.

FIG. 6 is a timing diagram illustrating the steps performed using thissolution for Scenario #1 when the source is eNB2 (which does not supportuse of the X2-GW 13) and the target is HeNB1 7-1 (which does support useof the X2-GW 13). At step s601 eNB2 5-2 discovers HeNB1 7-1 and at steps603, eNB2 5-2 initiates a TNL address discovery procedure by sending,to the MME 11, an S1 eNB Configuration Transfer message that includesthe global HeNB identifier (HeNB-ID1) of HeNB1 7-1 (as the intendedrecipient of the message) and its own global identifier (eNB-ID2) as themessage sender. The Configuration Transfer message also includes theTracking Area Indicator (TAI1) for HeNB1 and the TAI for eNB2 (TAI2). Inthis case, eNB2 does not support use of the X2-GW 13 and, therefore, theConfiguration Transfer message sent in step s603 does not include thenew Information element (IE1). At step s605, the MME 11 sends theConfiguration Transfer message to the HeNB1 7-1.

Due to the absence of the new IE1 in the received Configuration Transfermessage, HeNB1 7-1 (which does supports the use of the X2-GW 13)determines that the source base station (eNB2 5-2) does not support useof the X2-GW 13. Therefore, in step s607, HeNB1 7-1 responds by sendinga Configuration Transfer message back to the MME 11, that includes itsown TNL address (TNL-HeNB1). In step s609, the MME 11 sends the returnedConfiguration Transfer message to eNB2. In step s611, eNB2 uses the TNLaddress received in the Configuration Transfer message to establish adirect SCTP connection with HeNB1 and subsequent to that initiatesestablishment of a direct X2 connection with HeNB1.

Solution 1 (Scenario #2)

FIG. 7 is a timing diagram illustrating the steps performed using thissolution for Scenario #2 where the source is HeNB2 7-2 (which supportsuse of the X2-GW 13) and the target is eNB1 5-1 (which also supports useof the X2-GW 13). As shown in FIG. 7, at step s701 HeNB2 7-2 discoverseNB1 5-1. At step s703, the HeNB2 7-2 initiates a TNL address discoveryprocedure by sending, to the MME 11, an Si eNB Configuration Transfermessage that includes the global eNB identifier (eNB-ID1) of eNB1 5-1(as the intended recipient of the message) and its own global identifier(HeNB-ID2) as the message sender. The Configuration Transfer messagealso includes the Tracking Area Indicator (TAI1) for eNB1, the TAI forHeNB2 (TAI2) and a new Information element (IE1) that indicates thatHeNB2 7-2 supports use of the X2-GW 13. The new IE1 may be a single bitflag whose value indicates support or non-support for the X2-GW 13. Atstep s705, the MME 11 sends the Configuration Transfer message to theeNB1 5-1.

In response to receiving the Configuration Transfer message, the eNB15-1 replies by sending, in step s707, a Configuration Transfer messageback to MME 11, identifying its own TNL address (TNL-eNB1) and includinga new IE (IE1) that indicates that the target eNB1 5-1 supports use ofthe X2-GW 13. In step s709, the MME 11 sends the returned ConfigurationTransfer message to the HeNB2 7-2. In step s711, the HeNB2 determinesfrom the new IE1 in the returned Configuration Transfer message thattarget eNB1 supports use of the X2-GW 13.

Typically, HeNB2 will have registered with the X2-GW 13 at the time ofpower-up, and so there is no need for HeNB2 to register again with theX2-GW 13. Accordingly, in step s713, the source HeNB2 sends (over theSCTP connection already established between HeNB2 and X2-GW 13) an X2Setup Request message to the X2-GW 13, which message includes a new IE(IE2) containing the RNL-ID for eNB1 (which HeNB2 obtains when itdiscovers eNB1) and the TNL address of eNB1 (TNL-eNB1) which HeNB2received in step s709. In step S715, the X2-GW 13 uses the received TNLaddress of eNB1 to establish an SCTP connection with eNB1. In step S717,the X2-GW 13 forwards the X2 Setup Request message received from HeNB2to eNB1. Although not shown in FIG. 7, the target base station (eNB1)determines the identity of the source base station (HeNB2) from theRNL-ID of the source base station contained within the X2 Setup Requestand will respond with an X2 Setup Response message (not shown) whichwill be returned to HeNB2 via the X2-GW. If desired, the source basestation (HeNB2) could use new IE5 instead of IE2, in which it may alsoinclude the RNL ID and/or TNL Addresses pertaining to a target basestation In all subsequent X2 AP messages sent between eNB1 and HeNB2 viathe X2-GW 13, the sender includes (for example in new IE4 or new IE5)the RNL-ID of the intended recipient and its own RNL-ID so that theX2-GW 13 can use the intended recipient's RNL-ID to route the message tothe correct base station over the correct SCTP connection and so thatthe recipient knows the identity of the sending base station.

FIG. 8 is a timing diagram illustrating the steps performed using thissolution for Scenario #2 where the source is HeNB1 7-1 (which supportsuse of the X2-GW 13) and the target is eNB2 5-2 (which does not supportuse of the X2-GW 13). As shown in FIG. 8, at step s801 HeNB17-(discovers eNB2 5-2. At step s803, the HeNB1 7-1 initiates a TNLaddress discovery procedure by sending, to the MME 11, an S1 eNBConfiguration Transfer message that includes the global eNB identifier(eNB-ID2) of eNB2 5-2 (as the intended recipient of the message) and itsown global identifier (HeNB-ID1) as the message sender. TheConfiguration Transfer message also includes the Tracking Area Indicator(TAI2) for eNB2, the TAI for HeNB1 (TAI1) and a new Information element(IE1) that indicates that HeNB1 7-1 supports use of the X2-GW 13. Thenew IE1 may be a single bit flag whose value indicates support ornon-support for the X2-GW 13. At step s805, the MME 11 sends theConfiguration Transfer message to eNB1 5-1.

In response to receiving the Configuration Transfer message, the eNB25-1 ignores the new IE in the received Configuration Transfer message—aseNB2 is a legacy eNB and so does not know how to interpret this IE.Accordingly, eNB2 replies by sending, in step s807, a ConfigurationTransfer message back to the MME 11, identifying its own TNL address(TNL-eNB2). In step s809, the MME 11 sends the returned ConfigurationTransfer message to HeNB1 7-1. In step s811, HeNB2 determines from theabsence of the new IE in the returned Configuration Transfer messagethat target eNB2 does not support use of the X2-GW 13. Accordingly, instep s813, the source HeNB1 uses the received TNL address for eNB2 toestablish a direct SCTP connection with eNB2 and subsequent to that, instep s815, establishes a direct X2 connection with eNB2 over theestablished SCTP connection.

Please note that in Solution 1 (under any Scenario), if an eNB isinvolved in the X2 Setup then, based on the SCTP establishment and theRNL-ID details found in the new IE (e.g., IE3) pertaining to the eNB,the X2-GW has to create an entry in its mapping table for theRNL-ID-based forwarding.

Solution 2

This solution deals with the case where base stations register inadvance with their designated X2-GW. It is principally concerned withScenario #3 where one HeNB discovers another HeNB. However, it is alsoapplicable to Scenario #1 and Scenario #2 if macro base stations (eNBs)also pre-register with a designated X2-GW.

FIG. 9 is a timing diagram for Scenario #3, where source HeNB1 7-1(which supports use of X2-GW 13) identifies target HeNB3 7-3 (which doesnot support use of X2-GW 13). As shown, in step s901, source HeNB1pre-registers with X2-GW 13. This may be part of its power up sequencewhen HeNB1 is powered up, reset or reconfigured. At step s903, the X2-GW13 updates the data it maintains in its mapping table to identify thenew SCTP connection it has just established with HeNB1. In step s905,source HeNB1 discovers target HeNB3 and initiates an X2 setup procedureby sending, in step s907, an X2 Setup Request message to the X2-GW 13without performing a TNL address discovery procedure. The X2 SetupRequest message includes a new IE that identifies the RNL-ID of thetarget base station (HeNB3), which HeNB1 obtains in step s905 when itdiscovered HeNB3. The X2-GW 13 uses the received RNL-ID for HeNB3 to tryto locate a corresponding entry in its mapping table. If the X2-GW 13finds a corresponding entry in its mapping table, then the X2-GW 13forwards the received X2 Setup Request to HeNB3 over the SCTP connectionit has with HeNB3 and will return any X2 Setup Response messagesreceived back from HeNB3 to HeNB1, in order to establish the X2connection between HeNB1 and HeNB3.

However, in this example, HeNB3 is not registered with X2-GW 13 and soin step S909, the X2-GW 13 does not find a corresponding entry in itsmapping table. This may be because HeNB3 is a legacy device or becauseHeNB3 is registered with another X2-GW (not shown) or because HeNB3 isconfigured not to operate via any X2-GW. As a result, in step s911,X2-GW 13 sends an X2 Setup Failure message with a new cause of failureindicating that the target HeNB3 does not support operation with X2-GW13. In step s913, HeNB1 receives the X2 Setup Failure message anddetermines from the new cause that it will have to establish an X2connection directly with HeNB3. Accordingly, in step s915, HeNB1triggers a conventional TNL discovery process to determine the TNLaddress of HeNB3, so that an SCTP connection can be established betweenHeNB1 and HeNB3 in step s917 and so that a direct X2 connection can beestablished between HeNB1 and HeNB3 in step s919.

Solution 3

This solution also deals with the case where base stations register inadvance with their designated X2-GW. It is principally concerned withScenario #3 where one HeNB discovers another HeNB. However, it is alsoapplicable to Scenario #1 and Scenario #2 if macro base stations (eNBs)also pre-register with a designated X2-GW.

FIG. 10 is a timing diagram for Scenario #3, where source HeNB1 (whichsupports use of X2-GW 13) identifies target HeNB2 7-2 (which doessupport use of X2-GW 13). As shown, in step s1001, HeNBs (and ifapplicable eNBs) pre-register with their designated X2-GW (in this caseX2-GW 13). This may be part of each base station's power up sequence orwhen the base station is reset or reconfigured—and so will not bedefined as a single step performed at a single point in time. In steps1003, an SCTP connection is established between each registered basestation and the X2-GW 13. As the establishment of each SCTP connectionwill be performed at the time that the corresponding base stationregisters with the X2-GW 13, this step will also not be a single stepperformed at a single time. At step s1005, source HeNB1 discovers targetHeNB2. In response, source HeNB1 sends, in step s1007, a new X2Neighbour Notify message to the X2-GW 13, which message includes a newIE containing the RNL-ID of target base station (HeNB2). In step s1009X2-GW 13 uses the target RNL-ID contained in the new X2 Neighbour Notifymessage to check if this RNL-ID is already contained in its mappingtable. In this case, the RNL-ID for HeNB2 is in the mapping table(because HeNB2 is registered with X2-GW 13) and accordingly, in steps1011, the X2-GW 13 sends an X2 Neighbour ACK message that positivelyacknowledges to the source Base station (HeNB1) that the target basestation (HeNB2) is registered with X2-GW 13—and so an X2 connection canbe established via X2-GW 13. Accordingly, in response to receiving thispositive acknowledgement, source base station (HeNB1) initiates the X2setup procedure via the X2-GW 13 in step s1013. As before, this willinvolve HeNB1 sending to the X2-GW 13 an X2 Setup Request message. TheX2 Setup Request message will include a new IE (e.g. IE3) thatidentifies the RNL-ID of the target base station (HeNB2), which HeNB1obtained in step s1005 when it discovered HeNB2. In response toreceiving this X2 Setup Request message, the X2-GW 13 retrieves the TNLaddress for the target base station (HeNB2) from the target RNL-IDcontained in the X2 Setup request message and its stored mapping tableand then forwards the X2 Setup Request message to this target (HeNB2)using the retrieved TNL address. As before, the target base station(HeNB2) determines the identity of the source base station (HeNB1) fromthe RNL-ID of the source base station that is contained within the X2Setup Request and will return an X2 Setup Response message back to HeNB1via X2-GW 13 to set up the X2 connection between HeNB1 and HeNB2.

As can be seen from the above description, the source base station(HeNB1) is able to establish an X2 connection with the newly discoveredtarget base station (HeNB2) without performing a conventional S1 TNLaddress discovery procedure (thereby saving on processing load withinthe core network).

FIG. 11 is a timing diagram illustrating the situation when the targetbase station (in this example HeNB3) does not support use of X2-GW 13.Steps s1101 to s1107 correspond to steps s1001 to s1007 described abovefor FIG. 10, and so a description of these steps will be omitted. Instep S1109, the X2-GW 13 is not able to find the RNL-ID for HeNB3,because HeNB3 has not registered with X2-GW 13. Therefore, in steps1111, X2-GW 13 sends an X2 Neighbour Nack (negative-acknowledgement)message containing the target RNL address of HeNB3, back to HeNB1indicating to HeNB1 that the target base station (HeNB3) does notsupport use of X2-GW 13. Accordingly, in step s1113 HeNB1 triggers aconventional S1 TNL address discovery procedure to determine the TNLaddress for target base station HeNB3, so that it can then establish adirect SCTP connection with HeNB3 in step s1115 and then establish adirect X2 connection with HeNB3 in step s1117.

Solution 4

This solution is similar to solution 1, in that X2-GW information isexchanged between the source base station and the target base stationand a new Information Element (IE) is added in the X2 setup requestmessage to allow the X2-GW 13 to establish the X2 connection between thesource and target base stations. This solution is applicable to Scenario#1 and Scenario #2.

Solution 4 (Scenario #1)

FIG. 12 is a timing diagram illustrating the steps performed using thissolution for Scenario #1 where the source is eNB1 5-1 (which supportsuse of the X2-GW 13) and the target is HeNB2 7-2 (which also supportsuse of the X2-GW 13). Steps s1201 to s1209 and steps s1213 and s1219correspond to steps s501 to s509 and steps s513 and s519 described abovewith reference to FIG. 5, and a further description of these steps willtherefore be omitted. The difference between this solution and solution1 is that source eNB1 also registers with X2-GW 13 in step s1211 usingthe TNL address (TNL-GW) received from the target base station HeNB2.The advantage of this embodiment over Solution 1 discussed above is thatit simplifies the operation of the X2-GW 13, such that it will carry outthe same network connection process regardless of whether the basestation is an eNB or an HeNB. With Solution 1 described above, the X2-GWhas to support different procedures depending on whether the basestation is an HeNB or an eNB. In particular, with solution 1 when thereis no existing network connection between the X2-GW 13 and the targeteNB, the X2-GW has to create the mapping entries in its mapping tableusing the information contained in the X2 Setup Request message(received from the source base station) and then try to establish thenetwork connection with the eNB. With Solution 4 all the mapping tableentries will have been created before the X2-GW receives the X2 SetupRequest message.

Solution 4 (Scenario #2)

FIG. 13 is a timing diagram illustrating the steps performed using thissolution for Scenario #2 where the source is HeNB2 7-2 (which supportsuse of the X2-GW 13) and the target is eNB1 5-1 (which also supports useof the X2-GW 13). In step S1301, the source HeNB2 discovers target eNB1.At step s1303, the HeNB2 7-2 initiates a TNL address discovery procedureby sending, to the MME 11, an S1 eNB Configuration Transfer message thatincludes the global eNB identifier (eNB-ID1) of eNB1 5-1 (as theintended recipient of the message) and its own address (HeNB-ID2) as themessage sender. The Configuration Transfer message also includes theTracking Area Indicator (TAIL) for eNB1, the TAI for HeNB2 (TAI2) and anew Information element (IE1) that indicates that HeNB2 7-2 supports useof the X2-GW 13—this may be a single bit flag whose value indicatessupport or non-support for the X2-GW 13. In this embodiment, HeNB2 alsoincludes, within the S1 eNB Configuration Transfer message, the TNLaddress of its designated X2-GW 13 (TNL-GW) using the existing X2 TNLConfiguration Info IE. At step s1305, the MME 11 relays theConfiguration Transfer message to the eNB1 5-1.

If the target base station (eNB1) also supports operation through X2-GW13 (as it does in this case), then in response to receiving thisConfiguration Transfer message, the eNB1 uses the X2-GW TNL address(TNL-GW) contained within the received message to register itself withthe X2-GW 13 in step s1307 (please note that Step S1307 can take placeat any time between S1305 and S1315). Target eNB1 also replies to theConfiguration transfer message by sending, in step s1309, aConfiguration Transfer message back to MME 11, identifying its own TNLaddress (TNL-eNB1) and including a new IE (IE1) that indicates that thetarget eNB1 5-1 supports use of the X2-GW 13. In step s1311, the MME 11relays the returned Configuration Transfer message to HeNB2 7-2. In steps1313, the HeNB2 determines from the new IE1 in the returnedConfiguration Transfer message that the target eNB1 supports use of theX2-GW 13 and therefore, in accordance with this solution, will haveregistered with X2-GW 13. Accordingly, in step s1315, the source HeNB2sends (over the SCTP connection pre-established between HeNB2 and X2-GW13) an X2 Setup Request message to the X2-GW 13, which message includesa new IE (IE3) containing the RNL-ID for eNB1. Unlike in Solution 1,there is no need to send the TNL address of eNB1 in this message—as eNB1should have registered with the X2-GW 13 in step s1307. In step S1317,the X2-GW 13 uses the RNL-ID for eNB1 to look up its mapping table toidentify the corresponding TNL address for eNB1 and then forwards the X2Setup Request message received from HeNB2 to eNB1 using the retrievedTNL address. In response to receiving the X2 Setup Request message, thetarget base station (eNB1) determines the identity of the source basestation (HeNB2) from the RNL-ID of the source base station containedwithin the X2 Setup Request message and sends, in step s1319, an X2Setup Response message back to the X2-GW 13. This X2 Setup Responsemessage also includes the new IE (IE4) that identifies the RNL-ID of theintended recipient (HeNB2) for the message and its own RNL-ID. The X2-GW13 uses the intended recipient's RNL-ID to identify the correspondingSCTP connection over which the message should be forwarded. In this casethe message is forwarded to HeNB2 in step s1321. As before, in allsubsequent X2 AP messages sent between eNB1 and HeNB2 via the X2-GW 13,the sender includes (for example in new IE4 or new IE5) the RNL-ID ofthe intended recipient together with its own RNL-ID so that the X2-GW 13can use the intended recipient's RNL-ID to route the message to thecorrect base station over the correct SCTP connection and so that therecipient knows the identity of the sending base station.

In the above embodiments, a number of new Information Elements were usedin messages transmitted by the different base stations. Exemplaryinformation elements that can be used are given below in the followingtables:

New IE1 that can be added in the X2 TNL Configuration Info of TS 36.413V11.3.0

IE type and IE/Group Name Presence Range reference Semantics descriptioneNB X2 Transport 1 to Layer Addresses <maxnoofeNBX2TLAs> >TransportLayer M 9.2.2.1 Transport Layer Addresses for Address X2 SCTP end-point.— — — — — X2-GW Support M Boolean (TRUE, FALSE) Support indication ofX2-GW

Range bound Explanation maxnoofeNBX2TLAs Maximum no. of eNB X2 TransportLayer Addresses for an SCTP end-point. Value is 2. maxnoofeNBX2ExtTLAsMaximum no. of eNB X2 Extended Transport Layer Addresses in the message.Value is 16. maxnoofeNBX2GTPTLAs Maximum no. of eNB X2 GTP TransportLayer Addresses for an GTP end-point in the message. Value is 16.

In solution 1 a new IE (IE2) was added to the X2 Setup Request messagesent to the X2-GW. The table below illustrates an example of what IE2might contain. This new IE may be added to Section 9.1.2.3 of TS 36.423V11.4.0.

IE/ IE type Group and Semantics Assigned Name Presence Range referencedescription Criticality Criticality Message Type M 9.2.13 YES rejectGlobal eNB ID M 9.2.22 YES reject Served Cells 1 .. <maxCellineNB>Complete YES reject list of cells served by the eNB >Served Cell M 9.2.8— — Information >Neighbour 0 .. <maxnoofNeighbours> — —Information >>ECGI >>PCI >>EARFCN >>TAC Target Details >Global eNB M9.2.22 YES reject ID >eNB X2 O 1.. <maxnoofeNBX2TLAs> Transport LayerAddresses >>Transport M 9.2.2.1 Transport Layer Layer Address Addressesfor X2 SCTP end- point. >eNB X2 0.. Extended <maxnoofeNBX2ExtTLAs>Transport Layer Addresses >>IP-Sec O 9.2.2.1 Transport Layer TransportLayer Addresses for Address IP-Sec end- point. >>eNB 0.. GTP<maxnoofeNBX2GTPTLAs> Transport Layer Addresses >>>GTP M 9.2.2.1 GTPTransport Transport Layer Layer Address Addresses for GTP end-points(used for data forwarding over X2).

New IE3 that can be used in Solutions 1, 3 and 4 discussed above:

IE/ IE type and Assigned Group Name Presence Range reference Semanticsdescription Criticality Criticality Message Type M 9.2.13 YES reject ---Target Details >Global eNB M 9.2.22 YES reject ID

New IE4 that can be added to X2AP messages in general

IE/Group IE type and Assigned Name Presence Range reference Semanticsdescription Criticality Criticality Message Type M 9.2.13 YES rejectSource Details >Global eNB ID O 9.2.22 YES Ignore Target Details >GlobaleNB ID M 9.2.22 YES reject

New IE5 that may be added to X2AP messages in General.

IE/Group IE type and Semantics Assigned Name Presence Range referencedescription Criticality Criticality Message Type M 9.2.13 YES rejectSource Details >Global O 9.2.22 YES Ignore eNB ID Target Details >GlobalM 9.2.22 YES reject eNB ID >eNB X2 O 1.. <maxnoofeNBX2TLAs> TransportLayer Addresses >>Transport M 9.2.2.1 Transport Layer Layer Addressesfor X2 Address SCTP end-point. >eNB X2 0.. Extended<maxnoofeNBX2ExtTLAs> Transport Layer Addresses >>IP-Sec O 9.2.2.1Transport Layer Transport Addresses for IP- Layer Sec end-point.Address >>eNB 0.. GTP <maxnoofeNBX2GTPTLAs Transport > LayerAddresses >>>GTP M 9.2.2.1 GTP Transport Transport Layer Addresses Layerfor GTP end- Address points (used for data forwarding over X2).

In solution 3 an X2 setup failure message was sent with a new causevalue to indicate that the target base station does not support use ofthe X2-GW 13. The table below gives details of the changes to Section9.2.6 of TS 36.423 that will be needed to accommodate this new causevalue.

Semantics IE/Group Name Presence Range IE Type and Reference DescriptionCHOICE Cause Group M >Radio Network Layer >>Radio Network Layer MENUMERATED Cause ( Handover Desirable for Radio Reasons, Time CriticalHandover, Resource Optimisation Handover, Reduce Load in Serving Cell,Partial Handover, , . . . , ) >Transport Layer >>Transport Layer Cause MENUMERATED (Transport Resource Unavailable, Unspecified, No X2-GWSupport for target . . . ) >Protocol >>Protocol Cause M ENUMERATED(Transfer Syntax Error, ), . . . ) >Misc >>Miscellaneous Cause MENUMERATED (Control Processing Overload, , . . . )

The presence field of IE1, IE2, IE3, IE4 and IE5 can take eithervalue—i.e., Optional (O) or mandatory (M). Similarly, the AssignedCriticality field of IE2, IE3, IE4 and IE5 can again take eithervalue—i.e., reject or ignore.

Modifications and Alternatives

A number of detailed embodiments have been described above. As thoseskilled in the art will appreciate, a number of modifications andalternatives can be made to the above embodiments whilst stillbenefiting from the inventions embodied therein.

In the above embodiments, a mobile telephone based telecommunicationssystem was described. As those skilled in the art will appreciate, thesignalling techniques described in the present application can beemployed in other communications systems. Other communications nodes ordevices may include user devices such as, for example, personal digitalassistants, laptop computers, web browsers, etc.

In the above embodiments, (home) base stations and the X2-GW aredescribed as being addressed using their respective TNL addresses. Asthose skilled in the art will appreciate, other types of networkaddresses may be used instead, e.g. an Internet Protocol (IP) address.

It will be appreciated that an X2 communication link between two (home)base stations may be set up either on an end-to-end or a hop-by-hopbasis through the X2-GW. The embodiments described above assume ahop-by-hop operation, where an X2-GW terminates both SCTP and X2connections and hence maintains states for each X2 Setup (i.e. whichbase station is connected to which other base station). In the case ofend-to-end operation, the X2-GW operates more like an RNL level router,in which the X2 connection is terminated at the (H)eNBs and the X2-GWsimply relays the incoming X2AP message based on the targetidentity/address.

In the above embodiments, a base station that sent a message to anotherbase station through the X2-GW included the RNL address of the intendedrecipient of the message. This information allowed the X2-GW to identifythe correct SCTP connection over which it should send the message toreach the desired recipient. The message may also include the RNLaddress of the sending base station in some situations. This allowed thebase station that receives the message from the X2-GW to identify thesender of the message. As those skilled in the art will appreciate, itis not essential for the sending base station to include its own RNL ID.The X2-GW could add information in the forwarded message that identifiesthe sending base station to the recipient base station.

In the above embodiment, it was assumed that there is one TNL addressand one RNL-ID for a base station. In practice, a base station will usemultiple TNL Addresses for instance for the purpose of multi-homing,added security etc.

In the embodiments described above, the base stations each includetransceiver circuitry. Typically this circuitry will be formed bydedicated hardware circuits. However, in some embodiments, part of thetransceiver circuitry may be implemented as software run by thecorresponding controller.

In the above embodiments, a number of software modules were described.As those skilled in the art will appreciate, the software modules may beprovided in compiled or un-compiled form and may be supplied to the basestation or the X2-GW or to the mobile telephone as a signal over acomputer network, or on a recording medium. Further, the functionalityperformed by part or all of this software may be performed using one ormore dedicated hardware circuits. However, the use of software modulesis preferred as it facilitates the updating of the base stations,gateways, and the mobile telephones in order to update theirfunctionalities.

Various other modifications will be apparent to those skilled in the artand will not be described in further detail here.

This application is based upon and claims the benefit of priority fromUnited Kingdom patent application No. 1309970.0, filed on Jun. 4, 2013,the disclosure of which is incorporated herein in its entirety byreference.

1. A source base station comprising: at least one memory configured tostore instructions; at least one processor configured to execute theinstructions to: send, in an X2AP message towards an X2 gateway (X2 GW),a global eNB identifier (Global eNB ID) for use by the X2 GW in mappingto a transport network layer (TNL) address of the source base station;and send, towards a target base station, an eNB configuration transfermessage for discovery of a TNL address relating to the target basestation; and include an address of the X2 GW, in said eNB configurationtransfer message, when said source base station has an X2 GW supportcapability.